It is known in the art that in order to mix a milled asphalt product with cold ingredients in order to produce a hot-mix asphalt, firstly the cold ingredients are heated and dried in an internal rotary drum of a counter-flow drier with subsequent mixing, with a small or large percentage of a milled asphalt product and liquid asphalt cement in an outer mixing sleeve or in a “pugmill” separately with relation to the burner flame, to thereby form the hot-mix asphalt appropriate for use in asphalt paving applications.
One other process consists in placing the milled asphalt product to be heated and dried within a circular chamber with rotary axles provided with vanes with heating by electrical resistors or gas-fueled heaters and mixing with solid asphalt additive to produce a fully recycled hot-mix asphalt or placing the cold ingredients to be heated and dried within a circular chamber with rotary axles provided with vanes and heating by means of electrical resistors or gas-fueled heaters and mixing with liquid asphalt cement to produce a first grade hot-mix asphalt.
A circular chamber for heating, drying and mixing the cold ingredients with liquid asphalt cement for producing a first grade asphalt mix or for heating, drying and mixing a milled asphalt product with a solid asphalt additive in order to produce recycled hot-mix asphalt manufactured by the company SOMA—Empresa de Prestação de Serviços LTDA. is of the type that is schematically depicted in FIG. 1, comprising a circular chamber 2 mounted in common with the structure 17 in parallel to the horizontal position. The four rotary half-shafts provided with vanes are mounted to the structure 17 and provided with a speed varying means and are driven at rotary speeds of 3.3 rpm on heating and drying, of 6.6 rpm on mixing and of 9.9 rpm on leaving the chamber upon the hot-mix asphalt being uniformly finished, such half-shafts being connected to a vertical axle 16 driven by an appropriate reducer drive gear assembly 20 (not shown). The chamber is provided with electrical resistors or gas-fueled heaters 22 to provide thermal heating, by heat conduction, at the bottom and side parts of the chamber 2. The chamber 2 has at the bottom and sidewalls thereof plates 23 coated with high-hardness, friction-resistant cast steel 26 to receive the cold ingredients through the inlet 30 or the milled asphalt product also by way of inlet 30. One outlet 31 is provided at the bottom for letting out the recycled, uniform and finished first grade hot-mix asphalt taking more time to heat, dry and mix the cold ingredients with liquid asphalt cement, in order to produce a hot-mix asphalt and taking more time to heat, dry and mix the milled asphalt product with solid asphalt additive to produce a fully (100%) recycled hot-mix asphalt. The entire circular chamber is coated with heat insulating material 53 to avoid thermal energy losses. An outlet is provided at the topmost part to let out the filtered and clean gas through the flue 34 into the atmosphere. The circular heating, drying and mixing chamber 12 also supports a plurality of filter elements 32. Within the circular chamber 2, in the zone near the heating plates, the mixing vanes 40 scrape the bottom and side surfaces 23 to allow the transfer of heat, by radiation and convection, for heating and drying the cold ingredients or milled asphalt product. The circular chamber also accommodates a pipe 45 appropriate for injecting liquid asphalt cement, that is separated from the rotary shaft 25 by a sufficient distance to provide a space between the pipe 45 provided with spray nozzles 44 and the mixing vanes 40. The feeding, through inlet 30, of the cold ingredients or milled asphalt product also fed through inlet 30, into the circular chamber 2, is provided by a conveyor belt adequate for the cold ingredients or milled asphalt product 35 incoming from the cold ingredients silos/tanks 55 and milled product silos/tanks 57 (not shown). The cold ingredients or the milled asphalt product is heated and dried while circulating through the heating, drying and mixing shafts 25, clockwise, within the horizontal circular chamber, where the later is not provided with exhaust means for the combustion gases, and the particulate matter (dust and soot) therein is incorporated into the hot-mix asphalt by gravity. After weighing the cold ingredients, the liquid asphalt cement is also weighed in a cylindrical container 54 (not shown) and is transferred to the circular chamber by means of an asphalt pump 52 to be injected through the asphalt pipe 45 and the spray nozzles 44 into the hot-mix asphalt. In addition to mixing the cold ingredients with the liquid asphalt cement or the milled product with the solid asphalt additive, the vanes 40 also transport the hot-mix asphalt or the recycled homogeneous finished asphalt mix towards the outlet 31 of the circular chamber wherefrom the hot-mix asphalt or the recycled hot-mix asphalt is discharged from the circular chamber 2.
Conventional plants use rotary parallel single directional flow driers to heat and dry the milled asphalt product and rotary driers operating in counter-flow to heat and dry the cold ingredients to be mixed with liquid asphalt cement. However, the conventional plants that make use of counter-flow driers and/or parallel single directional flow to produce hot-mix asphalt evidence various disadvantages, for example the conventional plants are limited in terms of the percentage of milled asphalt that may be used to produce partially recycled hot-mix asphalt. The conventional plants also generate and emit smoke and other harmful emissions produced by the milled asphalt product. In conventional plants, the cold ingredients are received within the drying drum, and are consequently subjected to direct exposure to the flame and the hot stream produced by the process of combustion that takes place in the drier. In conventional plants, the “filler” charge leaves through an opening in the gate of the “filler” tank, and is directly sent to the “pugmill” or at the base of the hot elevator without any control of the “filler” amount. The conventional plants use a fuel temperature rectifier means as well as a flame adjusting means. However, the conventional hot-processing plants that make use of a drier with an internal drum for heating and drying the cold ingredients and an outer sleeve or chamber to mix the superheated cold ingredients with fine milled product and a second drying drum to heat to a lower temperature the coarse milled product and mix everything in the “pugmill”, are also subject to various disadvantages, for example, they are unable to control the final temperature of the mixture of superheated cold ingredients with the fine milled product, and they do not totally recycle (to a level of 100%) the milled product. The conventional plants introduce the milled product into different driers depending on the grade (coarseness or fineness) of the milled product. The conventional plants inject the same amount of hot asphalt, unexplainably, into the cold ingredients and into the milled asphalt product in the “pugmill”, in spite of the fact that one of these already has an asphalt content and the other has no asphalt content at all. The conventional plants receive, at the pugmill, milled products with temperatures different from one another. Furthermore, the conventional plants make use of an auger conveyor, and/or a fines recovery valve or similar means, such that the fine ingredient particles and the milled product particles, that are entrained in the hot and toxic gas exhaust stream, may return to the hot-mix asphalt process. The conventional plants heat the milled product by overheating the cold ingredients. Such contact burns the asphalt contained in the milled product, thereby jeopardizing the quality of the asphalt mixture and also increases the production of smoke and other harmful emissions. The conventional plants receive, in the “pugmill” the liquid asphalt cement, in the same amount, for the combination of fine milled product/cold ingredients/coarse milled product, for producing partially recycled hot-mix asphalt. The conventional plants use two conveyor types (inclined ramp and vertical ramp) for conveying hot substances at temperatures between 150° C. and 165° C. to the “pugmill”. The conventional plants do not have controlling means to control the temperature of the milled asphalt product, and the temperature of the mixture of superheated cold ingredients and fine milled product will be lowered upon contact with the coarse milled product, which is heated in a separate drier at a lower temperature. The conventional plants produce direct emissions of CO2 (carbon dioxide or carbon gas) which emissions increase the concentration of CO2 in the atmosphere, and contribute to aggravate the greenhouse effect. The conventional plants work using two driers, two burners that consume a large amount of diesel fuel or heavy oil and a combination of heavy oil and gasoline, particularly in the first drier, for heating the fine milled product by means of the superheating of the cold ingredients for the production of partially recycled hot-mix asphalt.
The conventional plants are unable to ensure that the final temperature of the hot-mix asphalt, using a high percentage of milled asphalt product, might be ideal, since there is mixed coarse milled product having a known temperature with superheated cold ingredients and fine milled product, without any control of temperature, which fact prevents the ideal situation that would consist in the production of hot-mix asphalt using a high percentage of milled product with an ideal known temperature.
It would be important to provide an apparatus and a method whereby the asphalt plant might be able to produce hot-mix asphalt using a full percentage of milled product. It would also be important that such plant might be able to heat and dry the cold ingredients without using the flame of a fossil fuel burner. It would further be important that such plant might be able to use combined solar thermal energy (CSTE), for example, with electric power or gas-fueled or biodiesel-fueled heaters 100 to produce, without exhaustion, hot-mix asphalt. it would also be important that such plant might be able to reduce the amount of smoke and other harmful emissions produced by the milled asphalt product. This plant would be more interesting if it were able to produce high-quality hot-mix asphalt. Furthermore, it would also be interesting that such plant might be able to cool down a large part of the thermal heating produced to provide the hot-mix asphalt. It would be even more important that such plant might be able to produce recycled hot-mix asphalt without needing to control the grade and amount of the milled asphalt product. It would be even more interesting that such plant did not require the introduction of the milled product into different driers in order to produce hot-mix asphalt.
It would be further interesting that the asphalt plant may be able to operate in the same manner of a, gravity collector with natural sedimentation, easily operable, with slow gas outflow velocity, allowing the particles of dust and soot to settle in consequence of the weight thereof, and further facilitating the small particles in suspension to also settle down and lay deposited on the hot-mix asphalt, leaving practically only the gas to cross at higher speed the outer surfaces of the filter elements.
It would be even more important that the plant for hot-mix asphalt to be able to replace the fossil fuels with efficient use of combined solar thermal energy (CSTE), with energy efficiency to produce lesser amounts of carbon gas, in order to produce hot-mix asphalt without however compromising the aspects of quality and of production.
It would be even more important if the hot-mix asphalt plant were capable of avoiding contaminating the cold ingredients or avoid soiling the plant at any time that the same is subjected to calibration.
It would be even more important that the plant for producing recycled hot-mix asphalt might be able to reduce the consumption of energy and the extraction of raw materials, and also reduce the emission of greenhouse gasses associated with generation of energy using fossil fuels.
It would be even more important that the asphalt plant might be able to produce hot-mix asphalt using cold ingredients with a size of up to 75 mm.
It would be even more important if the asphalt plant were able to produce fully recycled (100%) hot-mix asphalt using a full percentage of granular milled product, in chunks or pieces with sizes of up to 100 mm.
It would be interesting to provide an asphalt plant that would not use forced exhaust, fire, such as the direct flame of a burner, for heating and drying the cold ingredients in order to produce the hot-mix asphalt, and that would furthermore cost an equivalent price of a conventional gravity-type plant.
It would be interesting to provide an asphalt plant that might not require recirculation of a part of the hot and toxic gases arising from the combustion of a burner with air blowers.
It would be interesting to provide an asphalt plant capable of recovering and reusing the charge of a dumper truck filled with hot-mix asphalt that cooled down at the end of a pavement hole and crack-filling operation.
It would be interesting to provide an asphalt plant capable of avoiding to simultaneously inject equal amounts of liquid asphalt cement into the cold ingredients and into the milled asphalt product to produce recycled hot-mix asphalt.
It would be interesting to provide an asphalt plant capable of contributing positively to the environment, which latter is starting to show signs of serious depletion of its natural resources, by means of an economy of raw materials. This could constitute a contribution to the actions intended to reverse such serious problem.
It would be interesting to provide an asphalt plant that would not require forced mechanical exhaustion, cyclone means with static or dynamic separators, helical auger conveyors, fines recovery valve, extractor coils to return the dust and soot particulate matter from the cold ingredients and or from the milled asphalt product that are entrained with the exhaust gas stream in the drier.
It would be interesting to provide an asphalt plant that would not be subjected to limitations such as of a maximum stone size of 25 mm and that would also not be limited by the amount of the “filler” charge added to produce hot-mix asphalt.
It would be interesting to provide an asphalt plant able to perform the recycling process without using different temperatures of the milled asphalt product to produce hot-mix asphalt using a high percentage of milled product.
It would be interesting to provide an asphalt plant capable of heating, drying and mixing for a longer time the cold ingredients, the “filler” charge and the liquid asphalt cement to produce a hot-mix asphalt that would exhibit better quality and greater strength for purposes of asphalt-based paving operations.
It would be interesting to provide a plant for producing recycled hot-mix asphalt that would be able to heat, dry and mix for a longer time the milled product with solid asphalt additive to produce a fully recycled hot-mix asphalt, evidencing better quality and enhanced strength for asphalt-based road paving applications.
It would be interesting to provide a plant capable of making use of renewable energy resources, that would contribute less to the global warming effect, to produce hot-mix asphalt using a full percentage of milled product, mainly originating from defective road paving surfaces, that is, with the presence of potholes, cracks, wheel tracks, etc., to reuse the same for repairing such defects without requiring an entirely new asphalt recapping.
It would be interesting to provide an asphalt plant that would not require the removal of the heated and dried cold ingredients, which produces a sizable amount of dust and soils the plant facilities, from the tank where it is kept for discharging the asphalt mix every time that the plant needs to be shut down.
It would be interesting to be able to provide a plant for the production of hot-mix asphalt without needing to drop onto the floor or withdraw any cold mix used to calibrate the plant or without needing to inverse the direction of conveyance of the cold feed, or yet without contaminating the cold ingredients used for calibration.
It would be interesting to produce an asphalt plant capable of producing in one sole batch the load to be carried in a dumper truck, with finite weight and dosage of the cold ingredients, the “filler” charge and the liquid asphalt cement for the production of hot-mix asphalt.
It would also be very interesting to provide a plant capable of producing in one single batch the load to be carried by a dumper truck, with finite weight and dosage of the milled product and of the solid asphalt additive for producing 100% (one hundred percent) recycled hot-mix asphalt.
It would be even better if such plant were able to reprocess by re-milling the load of a dumper truck having returned from the worksite without discharging, upon arriving thereat under rainy weather with the consequent impossibility of applying the mixture.
It would be even better if such asphalt plant were able to perform recycling using a full percentage of milled product upon exposure thereof to the environment, in a wet condition, without compromising its quality. It would be even more desirable if such plant were capable of producing hot-mix asphalt without varying the amount of liquid asphalt cement and without varying the temperature of the cold ingredients.
It would be even better if such asphalt plant were able to correct the hot-mix asphalt upon a failure in the injection of liquid asphalt (either by excess or by default). It would be event better if such plant were able to produce hot-mix asphalt upon acquiring carbon credits by production in tons.
The main advantage of the present invention resides in the provision of an apparatus and a method allowing a plant to mix hot asphalt using a full percentage of milled product. One other advantage of the preferred embodiment of the invention resides in that the same produces hot-mix asphalt without using a fossil fuel burner and forced exhaust, fire, flame, for heating and drying the cold ingredients. One other significant advantage of the invention consists in that it provides for the return to the process, by gravity, without any means of mechanical conveyance, of the particulate matter held in suspension, which is indispensable for the stability and quality of the first-grade hot-mix asphalt or fully recycled hot-mix asphalt.
One other advantage resides in weighing the “filler” charge instead of receiving the same through an outlet gate of the “filler” tank falling directly into the “pugmill” or at the foot of the hot-mix elevator.
One other advantage of the invention resides in that there is produced thereby a high quality hot-mix asphalt. One further advantage consists in the production of hot-mix asphalt using combined solar thermal energy (CSTE). Yet another preferred advantage of the invention resides in that it is not necessary to recycle large amounts of gases produced by the drier.
Another advantage of the preferred embodiment of the hot-mix asphalt plant resides in the fact that the same does not operate with a plurality of driers for introducing and processing different grades of milled product.
One advantage of the invention is that it does not require different grades and proportions of milled product, the same does not need to be graded and provided in given proportions for purposes of control of the asphalt mix produced therewith.